The present invention relates to a method for surface treating a fluorinated contact lens. The process comprises treating the lens with a hydrogen-containing plasma to reduce the fluorine content of the surface layer, followed by oxidation of the surface to increase its oxygen and/or nitrogen content, thereby improving its wettability or providing chemical functionality for subsequent processing.
Contact lenses made from fluorinated materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. Regardless of their water content, both non-hydrogel and hydrogel fluorinated contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
The art has recognized that introducing fluorine-containing groups into contact lens polymers can significantly increase oxygen permeability. For example, U.S. Pat. No. 4,996,275 to Ellis et al. discloses using a mixture of comonomers including the fluorinated compound bis(1,1,1,1,3,3,3-hexafluoro-2-propyl)itaconate in combination with organosiloxane components. As described in U.S. Pat. Nos. 4,954,587, 5,079,319 and 5,010,141, the fluorination of certain monomers used in the formation of silicone hydrogels has been indicated to reduce the accumulation of deposits on contact lenses made from such materials. Moreover, the use of silicone-containing monomers having certain fluorinated side groups, i.e. xe2x80x94(CF2)xe2x80x94H, have been found to improve compatibility between the hydrophilic and silicone-containing monomeric units, as described in U.S. Pat. Nos. 5,387,662 and 5,321,108 to Kunzler et al. Other fluorinated contact lens materials have been disclosed, for example, in U.S. Pat. No. 3,389,012; U.S. Pat. No. 3,962,279; and U.S. Pat. No. 4,818,801.
Those skilled in the art have recognized the need for modifying the surface of fluorinated contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of a contact-lens surface improves the wettability of the contact lenses. This in turn is associated with improved wear comfort of the contact lens. Additionally, the surface chemistry of the lens can affect the lens""s susceptibility to deposition, particularly the deposition of proteins and lipids from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended-wear lenses, the surface is especially important, since extended-wear lenses must be designed for high standards of comfort over an extended period of time, without requiring daily removal of the lenses before sleep. Thus, the regimen for the use of extended-wear lenses would not provide a daily period of time for the eye to rest or recover from any discomfort or other possible adverse effects of lens wear during the day.
Contact lenses have been subjected to plasma surface treatment to improve their surface properties, with the intent to render their surfaces more hydrophilic, deposit resistant, scratch resistant, or otherwise modified. For example, plasma treatment to effect better adherence of a subsequent coating is generally known. U.S. Pat. No. 4,217,038 to Letter discloses, prior to coating a silicone lens with sputtered silica glass, etching the surface of the lens with an oxygen plasma to improve the adherence of a subsequent coating. U.S. Pat. No. 4,096,315 to Kubacki discloses a three-step method for coating plastic substrates such as lenses, preferably PMMA (polymethylmethacrylate) lenses. The method comprises plasma treating the substrate to form hydroxyl groups on the substrate in order to allow for good adherence, followed by a second plasma treatment to form a silicon-containing coating on the substrate, followed finally by a third plasma treatment with inert gas, air, oxygen, or nitrogen. Kubacki states that pretreatment with hydrogen, oxygen, air or water vapor, the latter preferred, forms hydroxy groups. Neither Letter nor Kubacki discusses the surface treatment of fluorinated contact lens materials in particular.
U.S. Pat. No. 4,312,575 to Peyman teaches the use of hydrogen/fluorocarbon gaseous mixtures to treat silicone lenses. In Example 2 of Peyman, polydimethylsiloxane lenses are initially treated with a 50% hydrogen/50% tetrafluoroethylene mixture, followed by an oxygen plasma treatment. Peyman states that when it is desired to utilize a halogenated hydrocarbon to perform the plasma polymerization process, hydrogen gas may be added to the halogenated hydrocarbon in order to accelerate the polymerization reaction. In particular, Peyman states that hydrogen may be added to the plasma polymerization apparatus in an amount ranging from about 0.1 to about 5.0 volumes of hydrogen per volume of the halogenated hydrocarbon. Peyman does not mention how to surface treat fluorinated materials sucha s flourosilicon hydrogel or highly fluorinated contact lens materials.
U.S. Pat. No. 4,631,435 to Yanighara et al. discloses a plasma polymerization process employing a gas containing at least one compound selected from halogenated alkanes, alkanes, hydrogen and halogens in specific combinations, the atomic ratio of halogen/hydrogen in the aforesaid gas being 0.1 to 5 and the electron temperature of the plasma in the reaction zone being 6,000xc2x0 K. to 30,000xc2x0 K. The resulting coating is, in particular, suitable as the protective film for magnetic recording media.
U.S. Pat. Nos. 5,153,072; 5,091,204; 5,034,265; and 4,565,083 to Ratner disclose a method of treating articles to improve their biocompatibility according to which a substrate material is positioned within a reactor vessel and exposed to plasma gas discharge in the presence of an atmosphere of an inert gas such as argon and then in the presence of an organic gas such as a halocarbon or halohydrocarbon gas capable of forming a thin, biocompatible surface covalently bonded to the surface of the substrate. The method is particularly useful for the treatment of vascular graft materials. The graft material is subjected to plasma gas discharge at 5-100 watts energy. Ratner does not discuss the surface treatment of a fluorinated contact-lens materials.
In view of the above, it would be desirable to provide a fluorinated contact lens with an optically clear, hydrophilic surface film that will exhibit improved wettability and biocompatibility. It would be further desirable to be able to surface treat a fluorinated hydrogel or non-hydrogel contact lens that would allow its use in the human eye for an extended period of time. In particular, it would be desirable to provide a high-Dk fluorinated ophthalmic lens capable of extended wear for continous periods of at least 24 hours and, more preferably, to provide a biocompatible lens capable of continous and comfortable wear for 3 to 30 days without unacceptable corneal swelling or other adverse effects.
The invention relates to a method of treating a fluorinated contact lens comprising the following steps:
(a) treating the polymer surface of the lens with a hydrogen-containing plasma to reduce the fluorine or Cxe2x80x94F bonding content of the lens; and
(b) plasma treating the reduced polymer surface with an oxidizing gas to increase its oxygen or nitrogen content.
This surface oxidation can improve the wettability or biocompatibility of the contact lens. Alternatively, the surface oxidation can provide chemical functionality for subsequent surface-modification processing such as the attachment of hydrophilic polymers (inclusive of oligomers or macromonomers) to the surface of the contact lens. The present invention is also directed to a contact lens that can be made by the above-described method.